protect the window(s) of face pieces, hoods, and helmets which do not unduly interfere
with the wearer's vision and permit easy access to the external surface of such
window(s) for cleaning.
(a) General. The wearer is restricted in movement by the hose or air
line and must return to a respirable atmosphere by retracing his route of entry. The
hose or air line is subject to being severed or pinched off.
(b) Type "A" hose mask respirator with blower. If the blower fails, the
units still provide an air supply and sufficient protection to permit the wearer to escape
although a negative pressure exists in the face piece during inhalation. Use is not
permissible in atmospheres immediately dangerous to life or health.
(c) Type "B" hose mask without blower. If the air supply fails, no
protection is provided the wearer. Limited to use in atmospheres not immediately
dangerous to life or health and from which the wearer can escape unharmed without aid
of the respirator.
(d) Type "C" air line respirators (continuous flow, demand, and
pressure demand types). The demand type produces a negative pressure in the face
piece on inhalation whereas continuous flow and pressure demand types maintain a
positive pressure in the face piece at all times and are less apt to permit inward leakage
of contaminants. Demand flow air-line respirators are for use in atmospheres
immediately dangerous to life or health, provided an auxiliary self-contained air supply is
worn to permit escape if the air supply fails.
2-21. COMBINATION ATMOSPHERE-SUPPLYING AND AIR-PURIFYING
Combination respirators will usually be made up on an air line respirator with an
air purifying attachment to protect the worker if the air line should fail; or, they may be
air-purifying respirators with small cylinders attached in case contaminant
concentrations exceed the capabilities of the air-purifying respirator. In assessing the
capabilities of combination respirators, limitations of the respective individual
components will determine the overall limitations of the combination. In other words,
the part (component) with the greater limitation will determine the overall limitations,
since the wearer may not change over, even if conditions should require it.
2-22. SELECTING THE PROPER RESPIRATORY PROTECTIVE DEVICE
Selection of the appropriate type of respiratory protective device is essential if the
health of the worker is to be protected. The following criteria should be considered
when making selections: